Macrophages in Crohn’s disease creeping fat are predominantly inflammatory and produce calprotectin

Crohn’s disease is characterized by transmural inflammation and therefore the mesenteric immune compartment has gained interest. However, its significance in Crohn’s disease is largely unclear. Macrophages are plastic cells that adapt their phenotype to environmental stimuli resulting in inflammatory and regulatory macrophage subsets. Hence, their distribution can reflect the overall nature of an immune infiltrate. We show that mesenteric macrophages contain two populations, characterized as CD11b-high and CD11b-dim. The CD11b-dim population is characterized by expression of regulatory markers CD206, CD200R, CD163, PD-L2, CD32. CD11b-high macrophages display an IFNγ induced signature and produce high levels of calprotectin. CD11b-dim and CD11b-high populations were comparable between Crohn’s disease and other indications in expression pattern, but the CD11b-high population was strongly overrepresented in this patient group. CD11b-high macrophages were isolated from the mesentery of patients undergoing bowel resection (n=12). CD11b-low macrophages were isolated from the same patients (n=10, remaining patients did not yield sufficient number of cells).